In biogas plants, bacteria are responsible for the decomposition and conversion of biomass into biogas. The bacteria have optimum living conditions only at a specific temperature at which the biochemical process proceeds effectively. For microbial conversion of biomass into biogas, therefore, it is necessary to keep the temperature in the septic tank constant. In mesophilic operation, the temperature lies ideally between around 35° C. and 40° C. Also, the biomass contained in the septic tank must be circulated in order to supply the bacteria with fresh nutrients.
Conventionally, cylindrical or flat heating bodies made from tubes with warm water flow are used as heat exchangers for heating the biomass in septic tanks. For example, German publication 28 21 790 or JP 3 161039 A describe heating bodies which heat the biomass in cooperation with agitators, so that the biomass is tempered as evenly and effectively as possible.
DE 10 2009 002 925 A1 discloses a heating and agitation register in which the heating register is positioned relative to an agitator such that a flow generated by the agitator can pass at least partially through and around the heating register. The heating register and the agitator here form a unit which can be inserted as one element into the septic tank. It is an advantage here that, on installation of the combined assembly, there is no need to ensure a suitable spacing between the agitator and heating register, and installation in a filled septic tank is possible. The heating register is made from tubes which are arranged in a plane transversely to the flow direction of the biomass, in order to enlarge the heat transfer area. One disadvantage of the heating register used here is that the intermediate spaces through which the biomass flows have a limited free cross-section on which undesirable deposits or temporary blockages can form.